Preparation of butadiene



Patented July 16, 1940 UNITED STATES PATENT OFFICE PREPARATION OF BUTADIENE No Drawing. Application November 18, 1938, Serial No. 241,164

I 4 Claims.

This invention concerns a process for the preparation of butadiene.

According to my process, butadiene-1.3 may be prepared simply and efficiently by passing a di- 5 chlorinated normal butane into a bath of molten metal chlorides maintained at a temperature between about 400 C. and about 600 C. Any dichlorinated normal butane, viz. 1.2-dichlorobutane, 2.3-dichlorobutane, 1.3-dichlorobutane,

or mixtures thereof, may be employed, either alone or in admixture with inert diluents such as nitrogen, etc. At reaction temperatures below about 525 C., the yield of butadiene is improved by mixing with the dichlorinated normal butane a small proportion of chlorine, i. e. 0.02

to 0.2 part by weight of chlorine per part of dichlorobutane, before or during the pyrolysis. The butadiene and other products formed in the process may be separated by fractional distillation or other suitable means.

The molten metal chloride bath in which the reaction is conducted comprises one or more of the chlorides of aluminum, potassium, sodium,

' iron, zinc, bismuth, and other metals, provided that such chlorides or mixtures of chlorides are fluid at the reaction temperature. A mixture of aluminum chloride and potassium chloride in equimolecular proportions is especially suitable since it has a low melting point and at the same time has a low volatility at any temperature attained in the process.

The following example will illustrate the invention, but is not to be considered as limiting its scope:

Example vaporized 1.2-dichlorobutane was passed at a uniform rate of 20 c. 0. per minute into a molten bath consisting of aluminum chloride and potassium. chloride in equimolecular proportions maintained at a temperature of about 550 C., the

vapor being introduced through a nozzle at a point 4 inches below the surface of the bath. The reaction products escaping from the molten chloride mixture were collected, passed through a water scrubber to remove hydrogen chloride formed in the process, and condensed. The condensate was then fractionally distilled to separate the butadiene. Some monochlor-butylene was also separated during the distillation. The yield of butadiene was 40.3 per cent of the theoretical, based on the dichlorobutane reacted.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the method herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed.

I claim:

1. The method of preparing butadiene which comprises passing a dichlorinated normal butane .into a bath of molten metal chlorides maintained at a temperature between about 400 C. and about 2. The method of preparing butadiene which comprises passing 1.2-dichlorobutane into a bath of molten metal chlorides maintained at a temperature between about 400 and about 600 C.

3. The method of preparing butadiene which comprises passing 1.2-dichlorobutane into a bath of molten metal chlorides maintained at a temperature of about 550 C.

4. The method of preparing butadiene which comprises passing a mixture of a dichlorinated normal butane and between-0.02 and 0.2 part by weight of chlorine into a bath of molten metal chlorides maintained at a temperature between about 400 C. and about 525 C.

CHARLES R. RUSSELL. 

